In recent years, with the development of the electronic products towards multi-function and miniaturization, and the development of the circuit substrate used towards multi-layer, high-density of wiring, high modulus and high-speed signal transmission, there is higher requirement for comprehensive performance of circuit substrate, that is, metal clad laminate, such as copper clad laminate.
For example, along with the development of high performance, high function and network of the information and communication equipments, and in order to treat and transmit large-capacity information with high speed, the operating signals tend to be high-frequency, and the electronic products have a rising used frequency, requiring not only the dielectric constant of a circuit substrate is smaller and smaller but also the dielectric constant of a circuit substrate has good stability and uniformity,
At present the copper clad laminate generally uses the glass fiber fabric as the reinforcing material. Woven material is used as glass fiber fabric (e.g. glass fiber fabric), due to the weaving in the woven material and the existing cross-type node in cross section of the woven fiber, the insulating medium (such as a glass component) can't distribute evenly and the dielectric constant of the circuit substrate isn't isotropic in X, Y and Z directions (wherein, X, Y and Z directions respectively refers to the direction of the circuit substrate along length, width and thickness), that is, there is the difference of the dielectric constant in X and Y directions. When such high-frequency signal is transmitted in the high frequency circuit substrate, the electromagnetic waves is transmitted not only in the X and Y directions, but also in the Z-direction, the attenuation of the signal is generated because of the difference the dielectric constant in X, Y and Z directions, which influence the stability of the signal transmission. In order to making the signal to transmit evenly and stably, there should be reduce the difference of medium distribution in X, Y and Z directions in the circuit substrate.
In addition, along with the increase of the circuit interconnection density of the electronic products, the requirements for the circuit substrate's dimensional stability become greater and greater; in order to reduce the thermal stress produced in the thermal shock in the process of making circuit substrates and meet the component's precise alignment holes in the installation and assembly process, CTEs (Coefficient of Thermal Expansion) of the circuit substrate in X, Y and Z directions (wherein, X, Y and Z directions respectively refers to the direction of the circuit substrate along length, width and thickness) should be as small as possible. Particularly for the circuit substrate used for IC packages, CTEs in X and Y directions should be close to that of silicon chips (3 ppm/° C.) as possible, because the chips can be damaged by the strong stress-strain produced during the environmental cold-thermal shock if the difference between CTE of the circuit substrate and CTE of the chip packaged in the laminate is too large.
At present, the copper clad laminate (FR-4) usually uses glass fiber fabric as a enhancement material, CTEs of the copper clad laminate in X and Y directions are between 16˜18 ppm/° C. due to the ratio between the glass fiber fabric and the resin in the laminates.
In order to reduce CTEs in X and Y directions, U.S. Patent Application US20040037950A1 proposed to use thin glass film to replace the glass fiber fabric to manufacture the copper clad laminate. This patent application declared a multi-layer board by the glass film, a resin layer and a copper layer, but it can't declare how to get good adhesion between the surface of the glass film and the resin layer. Because the surface of the glass film is smooth, a good binding force between the resin layer and the glass film can't be formed, which causes the copper wire along with the resin layer to come off easily from the glass film, which further causes the reliability of the copper clad laminate manufactured by this method is low during the process of assembly and usage, and also can cause the electronic products to be scrapped.